The present disclosure relates to subject monitoring. More particularly, the present disclosure is directed to determining and/or controlling a condition of a subject using measures of cardiac activity.
Myocardial ischemia (“MI”) refers to the condition when blood flow to the heart muscle is substantially decreased due to partial or complete blockage of coronary arteries. This reduces oxygen supply to the heart, resulting in heart muscle damage that in turn reduces the ability to pump blood efficiently. If ischemia is severe or prolonged, it may lead to more severe consequences, such as fatal tachy-arrhythmic events. Therefore, early diagnosis and risk stratification of patients with acute or long-term MI is essential to guide prompt interventions necessary to obtaining optimal clinical outcomes.
Presently, electrocardiographic ST-segment monitoring using body surface leads is widely used to detect acute MI. Specifically, the ST-segment is a flat, isolectric section of the electrocardiogram (“ECG”) signal, representing the interval between ventricular depolarization and repolarization found between the end of the S-wave, or the J-point, and the beginning of the T-wave. In the standard 12-lead configuration, ST-segment deviation is the most commonly used determinant of ongoing ischemia, and a strong predictor of the associated mortality. However, the sensitivity in detecting acute MI using this previous approach remains inadequately low. Whether due to the variability of the ischemia-induced changes in various ECG leads, as evidenced by body surface potential mapping, or the inaccuracy in detecting elevated J-points, body surface ECGs may not reveal sub-endocardial, and even severe transmural ischemia.
With the advent of implantable cardioverter defibrillators (“ICD”), defibrillation of ventricular tachy-arrhythmias has resulted in significant improvements in survival. Recent evidence also suggested that continuous monitoring of a patient's ST-segment changes in intra-cardiac electrograms may allow an implanted device to detect acute closure of a coronary artery, which could lead to a reduction in symptom-to-door time and thereby potentially improved clinical outcomes. In addition, it has been recently shown that the high-risk period for sudden death of patients who survive an acute MI extends beyond the hospitalization period, mostly due to recurrent MI or extension of the infarcted area. These results imply that early detection of MI, either in the ambulatory ECG, or from an implantable device, can provide significant therapeutic potential for high-risk patients.
Hence, in light of the above, there remains a need for systems and methods that can accurately detect myocardial disease, such as a acute or chronic ischemia.